The trend in the circuit protection industry is currently toward complete circuit protection which is accomplished by the addition of supplemental protection apparatus to standard overcurrent protective devices, such as molded case circuit breakers. In the past, when such auxiliary protection apparatus or other circuit breaker accessories were combined with a standard circuit breaker, the accessories were usually custom-installed at the point of manufacture. The combined protective device, when later installed in the field, could not be externally accessed for inspection, replacement or repair without destroying the integrity of the circuit breaker interior. An example of one such factory installed circuit breaker accessory is found in U.S. Pat. No. 4,297,663 entitled "Circuit Breaker Accessories Packaged in a Standardized Molded Case".
A more recent example of a circuit breaker including additional accessories is found in U.S. Pat. No. 4,622,444 entitled "Circuit Breaker Housing and Attachment Box" which allows the accessories to be field-installed within the circuit breaker without interfering with the integrity of the circuit breaker internal components. This is accomplished by mounting the accessories within a recess formed in the circuit breaker enclosure cover.
An electronic trip actuator which is mounted within the circuit breaker enclosure is described within U.S. Pat. No. 4,679,019 entitled "Trip Actuator for Molded Case Circuit Breakers". The circuit breaker actuator responds to trip signals generated by an electronic trip unit completely contained within a semi-conductor chip such as that described within U.S. Pat. No. 4,589,052. The development of a combined trip actuator for both overcurrent protection as well as accessory function is found within U.S. Pat. No. 4,700,161 entitled "Combined Trip Unit and Accessory Module for Electronic Trip Circuit Breakers".
A shunt trip accessory unit allows the circuit breaker operating mechanism to be articulated to separate the circuit breaker contacts, usually to perform a tripping function for electrical system control and protection. One such shunt trip accessory unit is described within U.S. Pat. No. 4,786,885 entitled "Molded Case Circuit Breaker Shunt Trip Unit". An auxiliary switch accessory unit allows an operator to determine the "ON" or "OFF" conditions of a molded case circuit breaker contacts at a remote location by means of an audible alarm or visible display. One such auxiliary switch unit is described within U.S. Pat. No. 4,794,356 entitled "Molded Case Circuit Breaker Auxiliary Switch Unit". A more recent example of a combined overcurrent trip actuator and multiple accessory unit is described within U.S. Pat. No. 4,788,621 entitled "Molded Case Circuit Breaker Multiple Accessory Unit" which combined overcurrent trip actuator and multiple accessory unit requires a separate mounting recess within the circuit breaker cover to house the printed wire board that carries the accessory control circuit.
U.S. Pat. No. 4,806,893 describes a molded case circuit breaker actuator-accessory unit wherein the integrated overcurrent trip actuator and multiple accessory unit containing the control electronics and mechanical interface components are contained on a single structure mounted within a single recess.
For purposes of this disclosure, an "electronic circuit breaker" shall mean a molded case circuit breaker that contains an electronic trip unit within a common enclosure with the operating mechanism and the interruptible contacts. A bell alarm unit is a useful accessory when such an electronic circuit interrupter is used within an industrial environment and it is important to know when a piece of manufacturing equipment has been shut down due to interruption of the electric power either by manual or automatic intervention. A space problem is involved in providing an electronic circuit interrupter with a bell alarm unit when the electronic circuit interrupter already contains more than one accessory device. Often times a user would have to select between accessories in view of the limited available space.
U.S. Pat. No. 4,939,490 entitled "Molded Case Circuit Breaker Bell Alarm Unit" describes a compact bell alarm unit that is attached to the side of the combined trip unit and accessory module described within U.S. Pat. No. 4,700,161. The bell alarm unit is attached to a remote bell alarm by means of three wire conductors that could extend a considerable distance from the site of the circuit breaker. This long length of wire conductor exhibits a high degree of strain on the connections between the ends of the wire conductors and the pin connectors on the microswitch used within the bell alarm unit. Encapsulating the connections and the microswitch provides limited strain relief to the connections. Upon long periods of continuous usage, the wire conductors could become loosened within the plastic material and exert increased strain on the electrical connections. All the aforementioned U.S. Patents which represent the advanced state of the art of circuit protection devices are incorporated herein for reference purposes.
One purpose of this invention is to provide a modular bell alarm unit that is attachable to a trip unit and accessory module that will not generate strain on the electrical connections between the wire conductors and the microswitch pin connectors.